1. Field of the Invention
The present invention relates to a semiconductor storage device including a nonvolatile memory such as a flash memory.
2. Description of the Related Art
In recent years, a flash memory card using a NAND type flash memory has been used as a storage medium for various types of portable information terminals such as a digital camera.
For the NAND type flash memory, memory cells which are disposed adjacent to each other and which share a drain and source and which are connected in series with each other are regarded as a basic unit (NAND unit). One end of the series connection is connected to a bit line via a select gate (SD(D)) and the other end thereof is connected to a source line via a select gate (SG(S)). An aggregate of the cells connected to the same word line constitutes a page as a basic unit of write or read, and an aggregate of the pages held between the select gate on the side of the bit line and that on the side of the source line constitutes a block.
An erase operation is basically performed by a block unit described above. Therefore, when rewrite occurs with respect to a part of the block, a save operation of copying data that is not to be rewritten to another area is required. A technique of rewrite/erase is described, for example, in Jpn. Pat. Appln. KOKAI Publication No. 6-52691.
Moreover, a physical address on a flash memory in which data of a certain logical address exists is frequently changed. Therefore, it is necessary to prepare a logical address/physical address conversion table required for performing logical address/physical address conversion every time. The conversion table is prepared in the following procedure at the time of power activation. That is, a redundant portion of a top page of each block is searched, and the data of the logical address corresponding to the data stored in the block is confirmed. In this case, a logical address region of the redundant portion is read, and the logical address/physical address conversion table is prepared based on an obtained value. A technique of the logical address/physical address conversion table is described, for example, in Jpn. Pat. Appln. KOKAI Publication No. 10-124384.
Additionally, when a file is updated in a memory card using the NAND type flash memory, the data of a file main body has a relatively large amount of data, and therefore the save operation does not occur so often. However, for data of a file management region such as a file allocation table (FAT), directory, and subdirectory, rewrite by a sector unit occurs with a large frequency. Therefore, there is a problem that the above-described save operation frequently occurs and a file rewrite performance of a flash memory card is deteriorated. Therefore, there is a demand for presentation of a technique for enhancing the rewrite performance of the file.
Moreover, in recent years, there is a tendency for increase of a capacity of the flash memory, and there is a problem that a preparation time (i.e., activation time) of the logical address/physical address conversion table is considerably long. Therefore, there is a demand for the presentation of a technique in which even with the increase of the capacity of the flash memory, the activation time of the conversion table does not increase. Furthermore, there is a demand for the presentation of a technique in which the data can be updated with a simple write algorithm without using the logical address/physical address conversion table.